Image processing apparatus, control method therefor, and storage medium storing program

ABSTRACT

An image processing apparatus includes: a tomographic image acquisition unit that acquires a first tomographic image of a subject&#39;s eye captured at a first time point that is a past time point; a tomographic image capturing unit that acquires a second tomographic image of the subject&#39;s eye captured at a second time point later than the first time point; and an image display control unit that, if one image capturing region of an image capturing region of the first tomographic image and an image capturing region of the second tomographic image is larger than the other image capturing region, performs control to provide, on an image display portion, a display of both a tomographic image of only a partial region of the one image capturing region which is a corresponding region corresponding to the other image capturing region and a tomographic image of the other image capturing region.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an image processing apparatus thatprocesses an image obtained by performing imaging of a subject's eye, acontrol method therefor, and a storage medium storing a program thatcauses a computer to execute the control method.

Description of the Related Art

In diagnostic imaging in ophthalmology as an example, recent use of atomographic image in addition to an eye fundus image that has beenwidely used allows three-dimensional observation of an internal state ofa retinal layer of an eye of a subject (subject's eye). Thus, adiagnosis made by using a tomographic image is expected to be useful formaking a more accurate diagnosis of a disease.

The above-described eye fundus image is captured by using a funduscamera, scanning laser ophthalmoscope (SLO), or infrared (IR) rays, forexample. The above-described tomographic image is captured by using anoptical coherence tomography (OCT) instrument, for example.

In recent years, there have been provided apparatuses that enablefollow-up observation of the internal state of the retinal layer of asubject's eye by using the above OCT instrument, thus enablingobservation of the development of a disease or the postoperativeclinical course. In follow-up observation of a subject's eye, a newlyacquired tomographic image is compared with a tomographic image of thesame site acquired in the past. This comparison between the images istypically made by displaying the newly acquired tomographic image andthe tomographic image acquired in the past simultaneously (hereinafterreferred to as “follow-up display”). This follow-up display facilitatesa comparative understanding of corresponding portions from twotomographic images and is very useful for follow-up observation.

With improvements in technology, it has become possible for an OCTapparatus that captures a tomographic image to capture a tomographicimage of a wider region in a single imaging session. There are alsofacilities having a plurality of OCT apparatuses with different imagingperformance (for example, the size of an image capturing region whoseimage can be captured). For example, in Japanese Patent Laid-Open No.2014-14727, a technique is proposed in which, in the case where a regionwhose image can be captured is enlarged as a result of the improvedperformance of a tomographic image capturing apparatus, imagingconditions for a tomographic image to be captured for follow-upobservation are set.

In the case where follow-up observation of a subject's eye is carriedout, a follow-up display is most often used as described above. Forexample, in the case of a facility having a plurality of OCT apparatuseswith different sizes (dimensions) of image capturing regions, there is asituation in which a captured tomographic image whose image capturingregion is different in size from that of a tomographic image captured inthe past has to be used in follow-up observation of an eye of a subject.In this case, when an attempt to display all image regions of eachtomographic image within a predetermined follow-up display range ismade, one tomographic image is reduced or enlarged in size to bedisplayed because the sizes of the respective image capturing regionsare different. In this case, since two tomographic images have adifferent display scaling factor, for example, the thicknesses of crosssections of the subject's eye may not be accurately compared with eachother, raising a concern that this may make effective follow-upobservation difficult.

Thus, it is considered that the entirety of each tomographic image isdisplayed at an original scaling factor on a follow-up display screen.In this case, however, the tomographic image whose image capturingregion is large (wide) contains an image region not used for comparison,thereby making a comparative understanding of corresponding portionsbetween the tomographic images difficult and increasing the burden offollow-up observation on an examiner. In this regard, the techniquedisclosed in Japanese Patent Laid-Open No. 2014-14727 is a technique ofsimply setting imaging conditions for the case where a tomographic imagewhose image capturing region is enlarged with respect to a pasttomographic image is captured, and thus it is difficult to solve thisissue.

SUMMARY OF THE INVENTION

An image processing apparatus according to the present inventionincludes: a first tomographic image acquisition unit configured toacquire a first tomographic image of a subject's eye captured at a firsttime point that is a past time point; a first image capturing regionacquisition unit configured to acquire a first image capturing regionthat is an image capturing region of the first tomographic image; asecond tomographic image acquisition unit configured to acquire a secondtomographic image of the subject's eye captured at a second time pointlater than the first time point; a second image capturing regionacquisition unit configured to acquire a second image capturing regionthat is an image capturing region of the second tomographic image; and adisplay control unit configured to, if one image capturing region of thefirst image capturing region and the second image capturing region islarger than an other image capturing region that is different from theone image capturing region, perform control to provide, on a displayportion, a display of both a tomographic image of only a partial regionof the one image capturing region which is a corresponding regioncorresponding to the other image capturing region and a tomographicimage of the other image capturing region.

Furthermore, the present invention includes a control method for theabove-described image processing apparatus, and a storage medium storinga program that causes a computer to execute the control method.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating an example of a schematicconfiguration of an ophthalmological image processing system accordingto an embodiment of the present invention.

FIG. 2 illustrates an example of an internal configuration of atomographic image capturing unit illustrated in FIG. 1.

FIGS. 3A and 3B illustrate this embodiment of the present invention andillustrate relationships between tomographic images captured bytomographic image capturing apparatuses with a different size of animage capturing region, and their image capturing ranges.

FIG. 4 is a flowchart illustrating an example of a procedure in acontrol method for an ophthalmological image processing apparatusaccording to this embodiment of the present invention.

FIG. 5 illustrates this embodiment of the present invention andillustrates an example of a follow-up display in which tomographicimages whose image capturing regions have a different size are used.

DESCRIPTION OF THE EMBODIMENTS

Forms (embodiments) for implementing the present invention will bedescribed below with reference to the drawings. In the followingembodiments, an example will be described in which an ophthalmologicalapparatus that captures an image of an eye fundus portion of a subjectis applied as an image processing apparatus according to the presentinvention. Furthermore, in the following embodiments, although anexample will be described in which the eye fundus portion of the subjectis applied as an object to be examined, the present invention is notlimited to this. Any object to be subjected to imaging for a tomographicimage, for example, an anterior eye segment, such as a cornea,crystalline lens, or an iris, can be applied.

FIG. 1 is a schematic diagram illustrating an example of a schematicconfiguration of an ophthalmological image processing system 10according to an embodiment of the present invention.

As illustrated in FIG. 1, the ophthalmological image processing system10 includes an ophthalmological image processing apparatus 100, a localarea network (LAN) 200, and an image database 300.

The ophthalmological image processing apparatus 100 is connected to theimage database 300 that stores an image captured in the past (pastimage) via the LAN 200. In other words, the ophthalmological imageprocessing apparatus 100 is configured to acquire a past image from theimage database 300 and also to store a captured image in the imagedatabase 300 as a past image. As illustrated in FIG. 1, thisophthalmological image processing apparatus 100 includes an imagecapturing control unit 110, an eye fundus image capturing unit 120, anda tomographic image capturing unit 130.

The LAN 200 is a local area network that connects the ophthalmologicalimage processing apparatus 100 to the image database 300 in such amanner that they can communicate with each other.

The image database 300 is a database that stores various types of pastimages and the like.

Next, an internal configuration of the ophthalmological image processingapparatus 100 will be described.

The image capturing control unit 110 has a function of performingcentralized control of operations performed by the ophthalmologicalimage processing apparatus 100 and also a function of processing acaptured image or the like. For example, the image capturing controlunit 110 controls capturing of an eye fundus image of an eye fundusportion of a subject's eye performed by the eye fundus image capturingunit 120 and also controls capturing of a tomographic image of the eyefundus portion of the subject's eye performed by the tomographic imagecapturing unit 130.

The eye fundus image capturing unit 120 captures an eye fundus image ofthe eye fundus portion of the subject's eye on the basis of controlperformed by the image capturing control unit 110.

The tomographic image capturing unit 130 captures a tomographic image ofthe eye fundus portion of the subject's eye on the basis of controlperformed by the image capturing control unit 110.

Furthermore, the eye fundus image capturing unit 120 and the tomographicimage capturing unit 130 are connected to each other and are configuredso that a tomographic image of an intended region contained in an eyefundus image can be captured while the eye fundus image is beingcontinuously captured. Specifically, a tomographic image of an intendedregion on an eye fundus image can be captured by controlling apositional relationship between lasers used for capturing of therespective images.

Next, an internal configuration of the image capturing control unit 110will be described.

As illustrated in FIG. 1, the image capturing control unit 110 includesa tomographic image acquisition unit 111, an image storage unit 112, afirst image capturing region acquisition unit 113, a second imagecapturing region acquisition unit 114, an image capturing regioncomparison unit 115, an image display control unit 116, and an imagedisplay portion 117.

The tomographic image acquisition unit 111 acquires, from the imagedatabase 300, as a first tomographic image, a tomographic image of thesubject's eye captured at a first time point that is a past time point.Note that, as the first tomographic image, an image captured by, forexample, another tomographic image capturing unit other than thetomographic image capturing unit 130 can be used.

The image storage unit 112 stores the first tomographic image or thelike acquired by the tomographic image acquisition unit 111 and alsostores an eye fundus image captured by the eye fundus image capturingunit 120 and a tomographic image captured by the tomographic imagecapturing unit 130. Here, a tomographic image that is captured by thetomographic image capturing unit 130 and stored in the image storageunit 112 is a second tomographic image of the same subject's eyecaptured at a second time point later than the first time point at whichthe first tomographic image has been captured.

The first image capturing region acquisition unit 113 acquires a firstimage capturing region that is an image capturing region of the firsttomographic image stored in the image storage unit 112. Here, in thisembodiment, an aspect can be applied in which the first image capturingregion acquisition unit 113 acquires the first image capturing region ofthe first tomographic image by using, for example, the first tomographicimage and an eye fundus image that are stored in the image storage unit112. Specifically, in the case where this aspect is applied, forexample, the first image capturing region acquisition unit 113 aligns anintegrated image representing an eye fundus surface with the eye fundusimage stored in the image storage unit 112 and thereby acquires thefirst image capturing region of the first tomographic image on the eyefundus image. The integrated image is generated by performing anaveraging process on the first tomographic image in the depth direction.Then, the first image capturing region acquisition unit 113 acquiresinformation, such as the position and size, of the first image capturingregion, and outputs this information to the image capturing regioncomparison unit 115 as first image capturing region information.

The second image capturing region acquisition unit 114 acquires a secondimage capturing region that is an image capturing region of the secondtomographic image stored in the image storage unit 112. Here, in thisembodiment, an aspect can be applied in which the second image capturingregion acquisition unit 114 acquires the second image capturing regionof the second tomographic image by using, for example, the secondtomographic image and an eye fundus image that are stored in the imagestorage unit 112. Specifically, in the case where this aspect isapplied, for example, the second image capturing region acquisition unit114 aligns an integrated image representing an eye fundus surface withthe eye fundus image stored in the image storage unit 112 and therebyacquires the second image capturing region of the second tomographicimage on the eye fundus image. The integrated image is generated byperforming an averaging process on the second tomographic image in thedepth direction. Then, the second image capturing region acquisitionunit 114 acquires information, such as the position and size, of thesecond image capturing region, and outputs this information to the imagecapturing region comparison unit 115 as second image capturing regioninformation.

The image capturing region comparison unit 115 compares the first imagecapturing region acquired by the first image capturing regionacquisition unit 113 with the second image capturing region acquired bythe second image capturing region acquisition unit 114. Specifically,the image capturing region comparison unit 115 determines, on the basisof the first image capturing region information (position and size) readfrom the first image capturing region acquisition unit 113 and thesecond image capturing region information (position and size) read fromthe second image capturing region acquisition unit 114, whether oneimage capturing region of the first image capturing region and thesecond image capturing region is larger than the other image capturingregion that is different from the one image capturing region, or whetherthe one image capturing region is a region including the other imagecapturing region.

As a result of a comparison determination made by the image capturingregion comparison unit 115, if the above-described one image capturingregion is larger than the other image capturing region that is differentfrom the one image capturing region and includes the other imagecapturing region, the image display control unit 116 performs control toprovide, on the image display portion 117, a follow-up display of both atomographic image of only a partial region of the one image capturingregion which is a corresponding region corresponding to the other imagecapturing region and a tomographic image of the other image capturingregion. Specifically, for example, if the above-described one imagecapturing region is the second image capturing region, and if theabove-described other image capturing region is the first imagecapturing region, the image display control unit 116 performs control toprovide, on the image display portion 117, a follow-up display of boththe second tomographic image of only a partial region of the secondimage capturing region which is a corresponding region corresponding tothe first image capturing region and the first tomographic image of thefirst image capturing region. Furthermore, for example, if theabove-described one image capturing region is the first image capturingregion, and if the above-described other image capturing region is thesecond image capturing region, the image display control unit 116performs control to provide, on the image display portion 117, afollow-up display of both the first tomographic image of only a partialregion of the first image capturing region which is a correspondingregion corresponding to the second image capturing region and the secondtomographic image of the second image capturing region. In this way, ofthe first tomographic image and the second tomographic image, inaccordance with the size of the tomographic image whose image capturingregion is small, the image display control unit 116 performs control tochange a display range of the tomographic image whose image capturingregion is large.

The image display portion 117 provides a follow-up display of both thefirst tomographic image and the second tomographic image on the basis ofcontrol performed by the image display control unit 116.

Next, an internal configuration of the tomographic image capturing unit130 will be described.

FIG. 2 illustrates an example of an internal configuration of thetomographic image capturing unit 130 illustrated in FIG. 1.

First, a measuring optical system will be described.

An objective lens 135-1 is disposed opposite a subject's eye E. On itsoptical axis, light is split and directed into an optical path 351 of anoptical coherence tomography (OCT) optical system, an optical path 352for eye fundus observation and a fixation light, and an optical path 353for anterior eye observation, for respective wavelength bands, by afirst dichroic mirror 132-1 and a second dichroic mirror 132-2.

In the optical path 352, light reflected from an eye fundus of thesubject's eye E is guided by a perforated mirror 133 to a charge coupleddevice (CCD) 172 for eye fundus observation. Additionally, to theoptical path 352, light from a scanning laser ophthalmoscope (SLO) lightsource 173 for eye fundus observation and a fixation light 191 is guidedby a third dichroic mirror 132-3. Furthermore, in the optical path 352,lenses 135-3 and 135-4 are disposed, and the lens 135-3 is driven by amotor (not illustrated) to perform focusing for the fixation light 191and eye fundus observation. The SLO light source 173 emits light with acenter wavelength of 780 nm. The fixation light 191 generates visiblelight to prompt eye fixation of the eye of the subject.

In the optical path 353, constituent elements of an optical system foranterior eye observation are disposed from a lens 135-2 to an infraredCCD 171 for anterior eye observation. The constituent elements include aprism 140 and a lens 135-10. The infrared CCD 171 has sensitivity at awavelength of illumination light for anterior eye observation,specifically, at a wavelength of about 970 nm.

The optical path 351 is an optical path of the OCT optical system asdescribed above and is used for capturing a tomographic image of the eyefundus of the subject's eye E. More specifically, the optical path 351is an optical path for obtaining an interference signal for generating atomographic image. In the optical path 351, there are disposed a shutter136 for applying light to the subject's eye E only during imaging and anXY scanner 134 for scanning the eye fundus of the subject's eye E withlight. Although this XY scanner 134 is illustrated as one mirror, the XYscanner 134 performs scanning in two axes directions of X-axis andY-axis directions. In the optical path 351, lenses 135-5 and 135-6 arefurther disposed. The lens 135-5 is driven by a motor (not illustrated)to focus light from a light source 201 emitted from a fiber 131-2connected to a fiber coupler 206 on the eye fundus of the subject's eyeE. Through this focusing, light from the eye fundus of the subject's eyeE simultaneously forms an image in a spot pattern and enters a leadingend of the fiber 131-2.

Next, configurations of an optical path extending from the light source201 and a reference optical system will be described.

The light source 201 is a wavelength-swept light source capable ofvarying wavelength and emits light with a center wavelength of about1040 nm and a bandwidth of about 100 nm, for example. The light emittedfrom the light source 201 is guided to a fiber coupler 204 via a fiber202 and is split and directed into a fiber 131-1 for measuring theamount of light and into a fiber 205 for performing OCT measurement. Thelight emitted from the light source 201 passes through the fiber 131-1and is measured in terms of the power thereof by a power meter (PM) 203.The light having passed through the fiber 205 is guided to the fibercoupler 206. The fiber coupler 206 functions as a division unit thatdivides an optical path through which the light from the light source201 is transmitted into a reference optical path and a measuring opticalpath. The light from the light source 201 is split into a measuring beam(also referred to as an OCT measuring beam) and a reference beam by thefiber coupler 206. A splitting ratio of the fiber coupler 204 is 99:1,and a splitting ratio of the fiber coupler 206 is 90:10 (referencebeam:measuring beam).

The measuring beam split by the fiber coupler 206 is emitted from afiber leading end 137 via the fiber 131-2. In the fiber 131-2, ameasuring beam-side polarization adjustment unit 139-1 is provided.Also, in a fiber 131-3, a reference beam-side polarization adjustmentunit 139-2 is provided. These polarization adjustment units have someportions in which a fiber is routed in a loop and can adjust therespective polarization states of the measuring beam and the referencebeam by rotating the loop portions on an axis in a longitudinaldirection of the fiber to apply a twist to the fiber. In the tomographicimage capturing unit 130 in this embodiment, the polarization states ofthe measuring beam and the reference beam are adjusted and fixed inadvance. The emitted measuring beam passes through the measuring opticalsystem and scans a region in an intended range of the eye fundus of thesubject's eye E.

The reference beam split by the fiber coupler 206 is emitted from afiber leading end 138-1 via the fiber 131-3 and the reference beam-sidepolarization adjustment unit 139-2. The reference beam emitted from thefiber leading end 138-1 passes through dispersion compensation glass 121and is reflected by reference mirrors 123-1 and 123-2 on a coherencegate stage 122. Subsequently, the reference beam enters a fiber leadingend 138-2 and reaches a fiber coupler 126 via a fiber 124.

The coherence gate stage 122 functions as a change unit that changespositions of the reference mirrors 123-1 and 123-2 and adjusts anoptical path length of the measuring beam and an optical path length ofthe reference beam by such a function. The reference mirrors 123-1 and123-2 are disposed so that a position at which the optical path lengthof the measuring beam is equal to the optical path length of thereference beam is disposed around the subject. The coherence gate stage122 is driven by a motor (not illustrated) to respond to a difference orthe like in eye axial length of the subject's eye E.

The fiber coupler 126 functions as a combining unit that combines thereference beam having passed through the reference optical path with themeasuring beam having passed through the measuring optical pathincluding a fiber 125. Thus, the measuring beam and the reference beamhaving reached the fiber coupler 126 are combined into interferencelight. The interference light passes through fibers 127 and 128 and isconverted into an electrical signal (interference signal) by a balancedreceiver 129 that is a photodetector for detecting combined light.Interference signals output from the balanced receiver 129 are subjectedto typical reconstruction processing, and thus a tomographic image isgenerated and acquired.

Next, a follow-up display, which is one of features of the presentinvention, will be described with reference to FIGS. 3A to 5.

FIGS. 3A and 3B illustrate this embodiment of the present invention andillustrate relationships between tomographic images captured bytomographic image capturing apparatuses with a different size of animage capturing region, and their image capturing ranges.

On a display screen 310A illustrated in FIG. 3A, an eye fundus image311A, a tomographic image 314A, a tomographic image capturing region312A, and a position 313A of the tomographic image 314A in the eyefundus image 311A are displayed. Similarly, on a display screen 310Billustrated in FIG. 3B, an eye fundus image 311B, a tomographic image314B, a tomographic image capturing region 312B, and a position 313B ofthe tomographic image 314B in the eye fundus image 311B are displayed.

The tomographic image capturing region 312B illustrated in FIG. 3B islarger (wider) than the tomographic image capturing region 312Aillustrated in FIG. 3A. Because of this, an image capturing region ofthe tomographic image 314B illustrated in FIG. 3B is larger (wider) thanan image capturing region of the tomographic image 314A illustrated inFIG. 3A.

In the tomographic image 314B illustrated in FIG. 3B, an image region316B is a corresponding region corresponding to the image capturingregion of the tomographic image 314A illustrated in FIG. 3A (that is,the same region as the image capturing region of the tomographic image314A, of a subject's eye). Furthermore, in the tomographic image 314Billustrated in FIG. 3B, image regions 315B and 317B arenon-corresponding regions not corresponding to the image capturingregion of the tomographic image 314A illustrated in FIG. 3A (that is,other regions other than the image capturing region of the tomographicimage 314A, of the subject's eye). These image regions 315B and 317B areimage capturing regions whose tomographic image cannot be acquired in asingle imaging session by a tomographic image capturing apparatus thatcaptures the tomographic image 314A illustrated in FIG. 3A.

FIG. 4 is a flowchart illustrating an example of a procedure in acontrol method for the ophthalmological image processing apparatus 100according to this embodiment of the present invention.

First, in step S401, the tomographic image acquisition unit 111acquires, from the image database 300 via the LAN 200, as a firsttomographic image, a tomographic image of a subject's eye captured at afirst time point that is a past time point. The tomographic imageacquisition unit 111 that performs this process of step S401 constitutesa first tomographic image acquisition unit. Then, the tomographic imageacquisition unit 111 stores the acquired first tomographic image in theimage storage unit 112.

Subsequently, in step S402, the first image capturing region acquisitionunit 113 acquires a first image capturing region that is an imagecapturing region of the first tomographic image stored in the imagestorage unit 112. Here, in this embodiment, an aspect can be applied inwhich the first image capturing region acquisition unit 113 acquires thefirst image capturing region of the first tomographic image by using,for example, the first tomographic image acquired in step S401 andstored in the image storage unit 112 and an eye fundus image captured bythe eye fundus image capturing unit 120 and stored in the image storageunit 112. Specifically, in the case where this aspect is applied, forexample, the first image capturing region acquisition unit 113 aligns anintegrated image representing an eye fundus surface with the eye fundusimage stored in the image storage unit 112 and thereby acquires thefirst image capturing region of the first tomographic image on the eyefundus image. The integrated image is generated by performing anaveraging process on the first tomographic image in the depth direction.Then, the first image capturing region acquisition unit 113 acquiresinformation, such as the position and size, of the first image capturingregion, and outputs this information to the image capturing regioncomparison unit 115 as first image capturing region information.

Subsequently, in step S403, the tomographic image capturing unit 130captures, on the basis of control performed by the image capturingcontrol unit 110, a tomographic image of the subject's eye at a secondtime point later than the first time point at which the firsttomographic image has been captured, and acquires this as a secondtomographic image. The tomographic image capturing unit 130 thatperforms this process of step S403 constitutes a second tomographicimage acquisition unit. Then, the tomographic image capturing unit 130stores the acquired second tomographic image in the image storage unit112.

Subsequently, in step S404, the second image capturing regionacquisition unit 114 acquires a second image capturing region that is animage capturing region of the second tomographic image stored in theimage storage unit 112. Here, in this embodiment, an aspect can beapplied in which the second image capturing region acquisition unit 114acquires the second image capturing region of the second tomographicimage by using, for example, the second tomographic image acquired instep S403 and stored in the image storage unit 112 and an eye fundusimage captured by the eye fundus image capturing unit 120 and stored inthe image storage unit 112. Specifically, in the case where this aspectis applied, for example, the second image capturing region acquisitionunit 114 aligns an integrated image representing an eye fundus surfacewith the eye fundus image stored in the image storage unit 112 andthereby acquires the second image capturing region of the secondtomographic image on the eye fundus image. The integrated image isgenerated by performing an averaging process on the second tomographicimage in the depth direction. Then, the second image capturing regionacquisition unit 114 acquires information, such as the position andsize, of the second image capturing region, and outputs this informationto the image capturing region comparison unit 115 as second imagecapturing region information.

Subsequently, before the process of step S405 is performed, the imagecapturing region comparison unit 115 determines, on the basis of thefirst image capturing region information (position and size) read fromthe first image capturing region acquisition unit 113 and the secondimage capturing region information (position and size) read from thesecond image capturing region acquisition unit 114, whether one imagecapturing region of the first image capturing region and the secondimage capturing region is a region including the other image capturingregion that is different from the one image capturing region. Then, ifthe image capturing region comparison unit 115 determines that theabove-described one image capturing region is a region including theabove-described other image capturing region, the image capturing regioncomparison unit 115 proceeds to a subsequent step S405. Note that, ifthe image capturing region comparison unit 115 determines that theabove-described one image capturing region is not a region including theabove-described other image capturing region, the image capturing regioncomparison unit 115 does not proceed to the subsequent step S405, andthe process of the flowchart in FIG. 4 ends.

In step S405, the image capturing region comparison unit 115 determines,on the basis of the first image capturing region information (positionand size) read from the first image capturing region acquisition unit113 and the second image capturing region information (position andsize) read from the second image capturing region acquisition unit 114,whether the above-described one image capturing region is the same sizeas the above-described other image capturing region. That is, in stepS405, it is determined whether the first image capturing region and thesecond image capturing region are the same size.

As a result of a determination made in step S405, if the above-describedone image capturing region is the same size as the above-described otherimage capturing region (YES in S405), the process flow proceeds to stepS406. The case of proceeding to step S406 refers to the case where thefirst tomographic image and the second tomographic image are tomographicimages of the same site of the subject's eye captured at the same size.

In step S406, the image display control unit 116 performs control toprovide, on the image display portion 117, a follow-up display of bothall image regions of the first tomographic image and all image regionsof the second tomographic image.

On the other hand, as a result of a determination made in step S405, ifthe above-described one image capturing region is not the same size asthe above-described other image capturing region (that is, they have adifferent size) (NO in S405), the process flow proceeds to step S407.The case of proceeding to step S407 refers to the case where the firstimage capturing region that is an image capturing region of the firsttomographic image is different in size from the second image capturingregion that is an image capturing region of the second tomographicimage.

In step S407, the image capturing region comparison unit 115 determineswhether the first image capturing region acquired by the first imagecapturing region acquisition unit 113 is larger than the second imagecapturing region acquired by the second image capturing regionacquisition unit 114.

As a result of a determination made in step S407, if the first imagecapturing region acquired by the first image capturing regionacquisition unit 113 is larger than the second image capturing regionacquired by the second image capturing region acquisition unit 114 (YESin S407), the process flow proceeds to step S408.

In step S408, for example, the image display control unit 116 detects acorresponding region corresponding to the second image capturing regionof the second tomographic image from within the first image capturingregion of the first tomographic image and sets the corresponding regionas a display range of the first tomographic image. That is, the displayrange of the first tomographic image is set so as to be the same regionas the second image capturing region of the second tomographic imagewhose image capturing region is small.

Subsequently, in step S409, the image display control unit 116 performscontrol to provide, on the image display portion 117, a follow-updisplay of both the display range set in step S408 of the firsttomographic image and all image regions of the second tomographic image.

On the other hand, as a result of a determination made in step S407, ifthe first image capturing region acquired by the first image capturingregion acquisition unit 113 is not larger than (that is, is smallerthan) the second image capturing region acquired by the second imagecapturing region acquisition unit 114 (NO in S407), the process flowproceeds to step S410.

In step S410, for example, the image display control unit 116 detects acorresponding region corresponding to the first image capturing regionof the first tomographic image from within the second image capturingregion of the second tomographic image and sets the corresponding regionas a display range of the second tomographic image. That is, the displayrange of the second tomographic image is set so as to be the same regionas the first image capturing region of the first tomographic image whoseimage capturing region is small.

Subsequently, in step S411, the image display control unit 116 performscontrol to provide, on the image display portion 117, a follow-updisplay of both all image regions of the first tomographic image and thedisplay range set in step S410 of the second tomographic image.

If the process of step S406, the process of step S409, or the process ofstep S411 is completed, the process of the flowchart illustrated in FIG.4 ends.

FIG. 5 illustrates this embodiment of the present invention andillustrates an example of a follow-up display in which tomographicimages whose image capturing regions have a different size are used. Ona follow-up display screen 500 illustrated in FIG. 5, there aredisplayed an image display region 510A displaying, for example, atomographic image captured by a tomographic image capturing apparatus inwhich an image capturing region is narrow, and an image display region510B displaying, for example, a tomographic image captured by atomographic image capturing apparatus in which an image capturing regionis wide.

In the image display region 510A, an eye fundus image 511A and atomographic image 513A are displayed. Furthermore, in the eye fundusimage 511A, a position 512A of the tomographic image 513A in the eyefundus image 511A is displayed.

In the image display region 510B, an eye fundus image 511B and aposition 514B of a tomographic image acquired by the tomographic imagecapturing apparatus in the eye fundus image 511B are displayed. Also, atomographic image of a partial region of the tomographic image acquiredby the tomographic image capturing apparatus is displayed as atomographic image 513B. The partial region is a corresponding regioncorresponding to an image capturing region of the tomographic image513A. Furthermore, in the eye fundus image 511B, a position 512B of thedisplayed tomographic image 513B of the tomographic image acquired bythe tomographic image capturing apparatus in the eye fundus image 511Bis displayed.

In the example illustrated in FIG. 5, all image regions of thetomographic image captured by the tomographic image capturing apparatusin which an image capturing region is narrow are displayed as thetomographic image 513A. A partial region of the tomographic imagecaptured by the tomographic image capturing apparatus in which an imagecapturing region is wide is displayed as the tomographic image 513B. Thepartial region is the corresponding region corresponding to the imagecapturing region of the tomographic image 513A. As described above, in afollow-up display in which tomographic images whose image capturingregions have a different size are used, as for a tomographic imagecaptured by a tomographic image capturing apparatus in which an imagecapturing region is wide, only a region corresponding to a tomographicimage captured by a tomographic image capturing apparatus in which animage capturing region is narrow is displayed, and thus a follow-updisplay of only corresponding regions of two tomographic images comparedwith each other can be provided without changing scaling factors of thetwo tomographic images, enabling accurate and easy follow-up observationof a subject's eye.

That is, according to this embodiment, even in the case where follow-upobservation of the subject's eye is carried out using tomographic imageswhose image capturing regions have a different size, a comparativeunderstanding of corresponding portions between the tomographic imagescan be facilitated, thereby enabling a reduction in the burden offollow-up observation on an examiner.

Other Embodiments

In the above-described embodiment of the present invention, although theexample is described in which a tomographic image captured by thetomographic image capturing unit 130 is used as the second tomographicimage in step S403 in FIG. 4, the present invention is not limited tothis form. For example, the following form is applicable to the presentinvention. In the form, the tomographic image acquisition unit 111acquires, as the second tomographic image, a tomographic image capturedat a second time point later than a first time point at which the firsttomographic image acquired in step S401 has been captured, from theimage database 300. In the case of this form, the tomographic imageacquisition unit 111 that acquires the second tomographic imageconstitutes the second tomographic image acquisition unit.

Embodiment(s) of the present invention can also be realized by acomputer of a system or apparatus that reads out and executes computerexecutable instructions (e.g., one or more programs) recorded on astorage medium (which may also be referred to more fully as a‘non-transitory computer-readable storage medium’) to perform thefunctions of one or more of the above-described embodiment(s) and/orthat includes one or more circuits (e.g., application specificintegrated circuit (ASIC)) for performing the functions of one or moreof the above-described embodiment(s), and by a method performed by thecomputer of the system or apparatus by, for example, reading out andexecuting the computer executable instructions from the storage mediumto perform the functions of one or more of the above-describedembodiment(s) and/or controlling the one or more circuits to perform thefunctions of one or more of the above-described embodiment(s). Thecomputer may comprise one or more processors (e.g., central processingunit (CPU), micro processing unit (MPU)) and may include a network ofseparate computers or separate processors to read out and execute thecomputer executable instructions. The computer executable instructionsmay be provided to the computer, for example, from a network or thestorage medium. The storage medium may include, for example, one or moreof a hard disk, a random-access memory (RAM), a read only memory (ROM),a storage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™),a flash memory device, a memory card, and the like.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2015-126044, filed Jun. 23, 2015, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. An image processing apparatus comprising: a firsttomographic image acquisition unit configured to acquire a firsttomographic image of a subject's eye captured at a first time point thatis a past time point; a first image capturing region acquisition unitconfigured to acquire a first image capturing region that is an imagecapturing region of the first tomographic image; a second tomographicimage acquisition unit configured to acquire a second tomographic imageof the subject's eye captured at a second time point later than thefirst time point; a second image capturing region acquisition unitconfigured to acquire a second image capturing region that is an imagecapturing region of the second tomographic image; and a display controlunit configured to, if one image capturing region of the first imagecapturing region and the second image capturing region is larger than another image capturing region that is different from the one imagecapturing region, perform control to provide, on a display portion, adisplay of both a tomographic image of only a partial region of the oneimage capturing region which is a corresponding region corresponding tothe other image capturing region and a tomographic image of the otherimage capturing region.
 2. The image processing apparatus according toclaim 1, wherein, if the one image capturing region is larger than theother image capturing region and includes the other image capturingregion, the display control unit performs the control to provide thedisplay.
 3. The image processing apparatus according to claim 2,wherein, if the one image capturing region is the second image capturingregion, and if the other image capturing region is the first imagecapturing region, the display control unit performs control to provide,on the display portion, a display of both the second tomographic imageof only a partial region of the second image capturing region which is acorresponding region corresponding to the first image capturing regionand the first tomographic image of the first image capturing region. 4.The image processing apparatus according to claim 2, wherein, if the oneimage capturing region is the first image capturing region, and if theother image capturing region is the second image capturing region, thedisplay control unit performs control to provide, on the displayportion, a display of both the first tomographic image of only a partialregion of the first image capturing region which is a correspondingregion corresponding to the second image capturing region and the secondtomographic image of the second image capturing region.
 5. The imageprocessing apparatus according to claim 1, wherein, if the one imagecapturing region is the second image capturing region, and if the otherimage capturing region is the first image capturing region, the displaycontrol unit performs control to provide, on the display portion, adisplay of both the second tomographic image of only a partial region ofthe second image capturing region which is a corresponding regioncorresponding to the first image capturing region and the firsttomographic image of the first image capturing region.
 6. The imageprocessing apparatus according to claim 1, wherein, if the one imagecapturing region is the first image capturing region, and if the otherimage capturing region is the second image capturing region, the displaycontrol unit performs control to provide, on the display portion, adisplay of both the first tomographic image of only a partial region ofthe first image capturing region which is a corresponding regioncorresponding to the second image capturing region and the secondtomographic image of the second image capturing region.
 7. A controlmethod for an image processing apparatus, the control method comprising:a first tomographic image acquisition step of acquiring a firsttomographic image of a subject's eye captured at a first time point thatis a past time point; a first image capturing region acquisition step ofacquiring a first image capturing region that is an image capturingregion of the first tomographic image; a second tomographic imageacquisition step of acquiring a second tomographic image of thesubject's eye captured at a second time point later than the first timepoint; a second image capturing region acquisition step of acquiring asecond image capturing region that is an image capturing region of thesecond tomographic image; and a display control step of, if one imagecapturing region of the first image capturing region and the secondimage capturing region is larger than an other image capturing regionthat is different from the one image capturing region, performingcontrol to provide, on a display portion, a display of both atomographic image of only a partial region of the one image capturingregion which is a corresponding region corresponding to the other imagecapturing region and a tomographic image of the other image capturingregion.
 8. The control method for the image processing apparatusaccording to claim 7, wherein, in the display control step, if the oneimage capturing region is larger than the other image capturing regionand includes the other image capturing region, the control is performedto provide the display.
 9. The control method for the image processingapparatus according to claim 8, wherein, in the display control step, ifthe one image capturing region is the second image capturing region, andif the other image capturing region is the first image capturing region,control is performed to provide, on the display portion, a display ofboth the second tomographic image of only a partial region of the secondimage capturing region which is a corresponding region corresponding tothe first image capturing region and the first tomographic image of thefirst image capturing region.
 10. The control method for the imageprocessing apparatus according to claim 8, wherein, in the displaycontrol step, if the one image capturing region is the first imagecapturing region, and if the other image capturing region is the secondimage capturing region, control is performed to provide, on the displayportion, a display of both the first tomographic image of only a partialregion of the first image capturing region which is a correspondingregion corresponding to the second image capturing region and the secondtomographic image of the second image capturing region.
 11. The controlmethod for the image processing apparatus according to claim 7, wherein,in the display control step, if the one image capturing region is thesecond image capturing region, and if the other image capturing regionis the first image capturing region, control is performed to provide, onthe display portion, a display of both the second tomographic image ofonly a partial region of the second image capturing region which is acorresponding region corresponding to the first image capturing regionand the first tomographic image of the first image capturing region. 12.The control method for the image processing apparatus according to claim7, wherein, in the display control step, if the one image capturingregion is the first image capturing region, and if the other imagecapturing region is the second image capturing region, control isperformed to provide, on the display portion, a display of both thefirst tomographic image of only a partial region of the first imagecapturing region which is a corresponding region corresponding to thesecond image capturing region and the second tomographic image of thesecond image capturing region.
 13. A storage medium storing, in anon-transitory manner, a program that causes a computer to execute eachstep of the control method for the image processing apparatus accordingto claim 7.